Taking on the part comes with extra baggage for any British actor, given the status of Alec Guinness's portrayal of the same character in an acclaimed 1970s television series.

Le Carre, who appears briefly on screen, advised the movie's producers to choose Swedish director Tomas Alfredson to adapt the notoriously complicated story of betrayal for cinema after seeing his vampire film "Let the Right One In."

"The television series had needed seven episodes," said Le Carre in a statement. "And slice it how you will, television drama is still radio with pictures whereas feature film these days barely talks at all."

But he added that he believed Alfredson had succeeded in capturing the essence of his story in just over two hours.

Oldman shines as the taciturn Smiley, who is sacked from British intelligence after his boss orders an operation to recruit a Hungarian general which goes badly wrong.

But he quickly returns to the cloak-and-dagger world of agents, double agents, deceit and danger when it emerges that the Soviets have infiltrated Britain's spy agencies.

Alfredson seeks to recreate the sights and sounds of 1970s London and Eastern Europe, and explores deception between nations as well as betrayals on a personal, more painful level.

The cast includes John Hurt as his boss Control, and Colin Firth, Ciaran Hinds, Toby Jones and David Dencik as the four key spies who could be behind the treachery.

"LOVING HAND"

Oldman said he had tried to block out the pressure Guinness's performance in the original adaptation may have put on him.

"I tried not to really think about it," he told Reuters in Venice, where the movie is one of 22 films so far confirmed in the main competition lineup.

A "surprise" 23rd movie is to be screened on Tuesday.

"Not breathing over my shoulder, but with a loving hand on my shoulder," he added.

Oldman said he was not particularly interested in Cold War politics at the time the film was set in the 1970s, when he was a teenager.

"I wasn't really too interested what was going on politically, I was more interested in girls and football and David Bowie," he explained.

Asked what he thought of a melancholic film which is at times slow paced and demands close attention from audiences with its twists and turns, he replied:

"It's a real grown-up's movie and you have to sit and you have to listen. And I go to the cinema and even audiences are very different now. Very noisy people. And they're always checking their phones.

"My youngest boy who is 12 can watch a movie on an iPhone, but it isn't odd for him. I am appalled."

Le Carre played possibly the ultimate compliment to Oldman for his performance.

"If people write to me and say, 'How could you let this happen to poor Alec Guinness,' I shall reply that, if 'poor Alec' had witnessed Oldman's performance, he would have been the first to give it a standing ovation."

Tinker, Tailor, Soldier, Spy hits British theatres later in September.